As is known in the art, a thermoelectric (TE) material refers to a material capable of directly converting thermal energy into electrical energy and vice versa or capable of cooling a material when a current is flowing in a desired direction through the material. Such materials include, for example, heavily doped semiconductor materials. Thermoelectric devices are fabricated from TE materials and are widely used in microelectronics and in biotechnology. Thermoelectric devices have the potential to replace freon-based air conditioners and refrigeration cooling devices; and to utilize waste heat by converting the heat to electrical power.
TE devices may also be used to convert heat into electrical power. For use in both refrigeration and power generation applications, it is desirable to choose the materials, and their relative amounts, so that the thermoelectric figure of merit, ZT, is maximized.
The dimensionless thermoelectric figure of merit (ZT) is a measure of the effectiveness of the material for both cooling and power conversion applications and is related to materials properties by the following equation:
 ZT=S2σT/K,
where S, σ, K, and T are the Seebeck coefficient, electrical conductivity, thermal conductivity and temperature, respectively. The figure of merit (ZT) is a measure of how readily electrons (or holes) can convert thermal to electrical energy in a temperature gradient as the electrons move across a thermoelement. The highest useful Seebeck coefficients are found in semiconductor materials with a high density of states at the Fermi level and the Fermi level is located near a band edge. In theory, to maximize the thermoelectric figure of merit ZT, one would try to increase or maximize the Seebeck coefficient S, electrical conductivity σ and temperature T and minimize the thermal conductivity K. However, in practice, this is not so simple. For example, as a material is doped to increase its electrical conductivity (σ), bandfilling tends to lower the Seebeck coefficient S and the electronic contribution, Ke; the thermal conductivity K increases. At a given temperature, the thermoelectric figure of merit ZT for a given material is maximized at an optimum doping level. In most materials, the thermoelectric figure of merit ZT is maximized at doping levels of approximately 1019 cm−3. Since increasing (or decreasing) one parameter may adversely decrease (or increase) another parameter, it is generally difficult to achieve higher values for ZT. It should of course be appreciated that increasing σ increases Ke, but decreases S and vice-versa. Currently, the best commercial thermoelectric materials have a maximum ZT of approximately one. The ZT values are below one at temperatures both below and above the temperature at which they achieve the maximum value.
The thermoelectric figure of merit ZT in conventional (bulk) thermoelectric materials is also related to the thermoelectric materials factor (b*) which may be expressed as:b*=μm*3/2/KLin which:                μ is the carrier mobility;        m* is the density of states effective mass; and        KL is the lattice thermal conductivity.The precise relationship between the thermoelectric materials factor b* and the thermoelectric figure of merit ZT is relatively complex.        
Bulk thermoelectric devices are known, and test structures for testing these bulk devices have been designed, however these test structures are unacceptable for testing thick film thermoelectric devices. The bulk device test structures are not able to accept the films. More importantly perhaps, parasitics associated with bulk device test structures are too severe to allow for accurate measurements of thick film thermoelectric devices. By parasitics, we mean thermodynamically irreversible heat flows which act to reduce the amount of cooling possible. Examples of parasitics include, but are not limited to, radiative heat flow from the surroundings, heat flow thermally conducted along the lead wires of the Chr-Alu temperature measurement thermocouples to the cool region of the test structure, and the electrical contact resistance. The relative importance of each of the parasitics changes with the magnitude of the cooling. The test structure suitable for bulk samples are not matched in terms of their thermal, electrical, and geometrical properties. The radiation parasitics are relatively large compared to bulk. Electrical contact resistance can further increase the difficulty of carrying out accurate measurements. The fragile nature of some samples further complicates the testing of the thick film TE material. It would, therefore, be desirable to provide a device test structure which allows accurate testing and characterization of thermoelectric thick film materials and structures.